Activated cathode for electron discharge devices



R. R. BACK Sept. 26, 1950 ACTIVATED CATHODE FOR ELECTRON DISCHARGE DEVICES Filed Nov. 23, 1945 F/GZ.

Patented Sept. 26, 1950 ACTIVATED CATHODE FOR ELECTRON DISCHARGE DEVICES Raymond Richard Back, London, England, as-

signor, by mesne assignments, to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application November 23, 1945, Serial No. 630,338 In Great Britain December 3, 1943 Section 1, Public Law 690, August 8, 1946 Patent expires December 3, 1963 1 Claim. 1

The present invention relates to arrangements for activating the cathode in an electron discharge device.

In glow discharge tubes it is well known that the striking voltage at which the discharge commences can be lowered by coating the cathode with a metal having a low work function. A common method of doing this is to vapourise an appropriate metal held in a container (for example by heating the container by means of eddy currents) so that the metal is deposited on the cathode. the container by bombardment in a gaseous atmosphere.

If however the spacing between the anode and cathode is small, there may not be room t accommodate the container in a favourable position for deposition of the coating on the cathode, and in any case if this were possible, the field between the anode and cathode would be unduly influenced by the presence of the container.

The principal obiect of the invention is to overcome these difficulties.

The invention provides in an electron discharge device having an anode and a cathode. a method of activating the cathode which comprises perforating the anode, providing means independent of the anode for holding a metal of low work function outside the space between the anode and cathode, and. liberating the metal in such manner as to deposit it through the anode on to the cathode.

The invention also provides a method of making an electron discharge device having an anode and a cathode, which includes activating the oath. ode by vapourising a metal of low work function on to the cathode through perforationsin the anode, the metal being held in one or more containers separate from the anode and located outside any electric field capable of being established between the anode and cathode.

The invention further provides an electron discharge device comprising an envelope, and contained therein a cylindrical anode arranged coaxially inside a cylindrical cathode, one or more holes in the anode, and one or more corresponding containers arranged inside the anode opposite the holes and adapted to hold metal of a low work function employed for activating the oathode.

The invention will be explained in terms of an embodiment illustrated on the accompanying The metal may also be liberated from drawing, in which Fig. 1 shows a perspective view of the electrodes of a glow discharge tube (partly cut away to show the details), and Fig. 2 shows part of a radial section through the electrodes.

The electrodes of the tube are cylindrical and comprise a cathode I co-axiall surrounding an anode 2 inside the usual bulb or envelope (not shown). Both are mounted by suitable means (not shown) on the stem 3. The anode is perforated by a number of holes 4, and inside the anode behind each of these holes is mounted a container 5 for an appropriate cathode coating metal such as barium. The barium may then be vapourised, for example, by electron bombardment in a gas, and will be deposited through the holes 4 on to the inside surface of the cathode. The containers 5 are substantially screened by the anode from the electric field between the anode and cathode and therefore will not appreciably affect it.

Although the tube shown has cylindrical electrodes, substantiall the same method may be used if the anode and cathode were parallel plates, or were shaped in some other way. The containers would be arranged belirnd the anode so as to direct the vapourised metal on to the cathode through corresponding holes.

What is claimed is:

An electron discharge device that comprises a cylindrical cathode, a cylindrical anode coaxially mounted within said cathode and'provided with apertures, a container mounted adjacent said apertures and separated from the cathode by said anode, said container holdinga metal of low work function capable of being released upon heating of said container.

RAYMOND RICHARD BACK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS- Number Name Date 1,965,849 McIlvaine July 10, 1934 2,121,589 Espe June 21, 1938 2,232,002 Hays Feb. 18, 1941 FOREIGN PATENTS Number Country Date 54:7 645 Great Britain Sept. 4. 1942 

